For the purpose of producing, for example, automobile bodies, body parts are so positioned in relation to one another in a receiving device that locations to be worked, for example edges to be welded to one another, are located in the working range of the robot arm. The robot arms moves with the tool, in this case a welding tip, along the line at which the two workpieces are to be welded to one another. Frequently, these lines are not rectilinear, but are curved according to the form of the body, such that a robot control system programmed thereto the robot tip can follow this curved line.
It is to be noted in connection therewith that no body part is identical to another, because of the existence of tolerances, deformations and the like.
For this purpose, for the working of body parts an ideal body is first produced, which body is so worked and processed that tolerances are brought almost to zero. This highly precisely produced ideal body, which is also referred to as a measurement body or measurement body-shell, serves the purpose of programming the robot motion.
When a real body is to be worked, this real body is assigned to the robot, or positioned, and image recordings, for example of the contours to be welded together, are produced by means of a plurality of cameras, as a result of which the misalignment can be identified. There is produced therefrom a mean positional vector, which corresponds to an average displacement or twist of the actual contour in relation to the contour of the ideal body, and which is input to the control system of the robot.
Accordingly, the robot tip is moved according to the mean positional vector. This can have the consequence that the robot tip does not travel exactly along the contour, it being the case that the deviations of the motion of the robot tip from the the contour are not to be too great.